Finding. TDC How

sunshine

sunshine

Senior Member
What is the best way to find TDC on the flathead V8 . I need to do a leak down test. Thank you again BOB
 
I agree, zip tie large end centered in the combustion chamber. Establish a pointer of some type on the crank pulley. Rotate the engine until it contacts the zip-tie end and mark the pulley. Rotate in the opposite direction to again contact the zip-tie end and again mark the pulley. TDC is half-way between the two marks. Repeat several times to assure consistency. If you search you should find detailed instructions.
 
Thank you JSeery I. Searched for the instructions but could not find them. I have a suspect cylinder 3 that I want to do a leak down test on . I have not obtained the tester yet .No point in obtaining one if I can’t figure out TDC . Thank you BOB
 
Take a zip tie insert the thick end through the sparkplug hole so it ends up over piston center.
Turn engine clockwise until piston hits zip tie and stops...slow and nice no forcing it!!
Make a mark on pulley.
Turn engine the other direction until it stops...mark pulley.
Right between the 2 marks is TDC.
 
Here are a couple of links on the method within in this post.



https://www.fordbarn.com/forum/showpost.php?p=1771516&postcount=4


The zip tie needs to be pushed in so that it is beyond the valves and over the piston. Any place over the piston works. The zip tie head provides a hard stop approaching TDC from one direction of engine rotation by hand and then once again by rotating the engine in the opposite direction. TDC is half way between the two "stops".


Glenn
 
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As far as the leak down test goes, I would mark the crank pulley every 90 deg. One cylinder will be at TDC every 90 deg, so you just have to work your way through the firing order. Each cylinder it at TDC twice, only one of which is the compression stroke. It fairly easy to tell the compress stroke because of the air pushed out of the sparkplug hole.
 
Thanks. Everyone for your help I will give it a try . I’ve got a miss that I can’t put on the ignition . That is the reason for the leak down test Thanks. BOB
 
Leakdown may show a badly sealing valve but not a sticking one...putting a vacuum gauge on it will quickly give you a hint about what´s going on...just my 2c.
 
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